Shadow mask having apertures at intersections of barrel-shaped horizontal and pin-cushion-shaped vertical lines

ABSTRACT

In a cathode ray tube having a curved phosphor screen, a shadow mask having apertures therein and electron beam generating means for generating three in-line electron beams aligned in a horizontal direction, the apertures of the shadow mask are aligned in the form of barrel-shaped lines extending in a horizontal direction and are aligned in the form of pin-cushioned lines extending in a vertical direction. The apertures are circular at the central portion of the mask but become gradually elliptic as the peripheral portion of the mask is approached from its center, and the longer axis of the elliptic apertures are inclined at predetermined angles to a horizontal direction corresponding to their particular locations.

United States Patent Naruse et al.

[451 Dec.5, 1972 [54] SHADOW MASK HAVING APERTURES AT INTERSECTIONS OF BARREL- SHAPED HORIZONTAL AND PIN- CUSHION-SHAPED VERTICAL LINES [72] Inventors: Yohsuke Naruse; Ryosuke Ashiya; Takehiko Nii; Yuzo Fuse, all of Tokyo, Japan [73] Assignee: Sony Corporation, Tokyo, Japan [22] Filed: May 27, 1970 [21] Appl. No.: 40,868

[30] Foreign Application Priority Data May 31,1969 Japan ..44/421 43 [52] US. Cl. ..313/85 S, 313/92 B [51] Int. Cl ..H01j 29/06, l-lOlj 31/20, HOlj 29/80 [58] Field of Search ..,.313/92 B, 85 'S, 70 C [56] References Cited UNITED STATES PATENTS 3,109,117 10/1963 Kaplan ..3l3/80X 4/1956 Reed ..3l3/92BX 8/1960 Kaplan ..3l3/92B Primary Examiner-Robert Segal Attorney-Lewis l-l. Eslinger, Alvin Sinderbrand and Curtis, Morris & Safford [5 7] ABSTRACT In a cathode ray tube having a curved'phosphor screen, a shadow mask having apertures therein and electron beam generating means for generating three in-line electron beams aligned in a horizontal direction, the apertures of the shadow mask are aligned in the form of barrel-shaped lines extending in ahorizontal direction and are aligned in the form of pin-cushioned lines extending in a vertical direction. The apertures are circular at the central portion of the mask but become gradually elliptic as the peripheral portion of the mask is approached from its center, and

- the longer axis of .the elliptic apertures are inclined at predetermined angles to a horizontal direction corresponding to their particular locatio'ns.

5 Claims, 15 Drawing Figures PATENTEDBEB 5 I972 3, 705.322

sum u or 7 INVENTUR YOHSUKE NARUSE RYOSUKE ASH [YA TAKEH l KO N H YUZO FUSE PATENTEDBEB 51912 I 3.705.322

' sumsnr? Ii g- [7 x5 Y2 W) W Y2 v 1.\"vEA\'T0/ YOHSUKE NARUSE RYOSUKE ASHIYA TAKEHIKO YUZO FUSE ATTORNEYS BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to an improved shadow mask, and more particularly to a .color cathode ray tube in which an improved shadow mask is used to ensure that the electron beam strikes exactly on a color dot of the tube. I

2. Description of the Prior Art Conventional types of color cathode ray tubes comprise an electron gun for emitting an electron beam, a colorsc reen anda shadow mask or aperture grill for beam selection, in which each of the apertures perforated in the mask or grill is supposed to correspond exactly to each of the color dotsto cause the beams to strike precisely on predetermined .color dots for reproducing acolor picture. However, the beam does not strike thedots accuratelydue to certain causes that introduce improper masking and or misconvergence. This effect is worse in the peripheral areas of the screen than at the center. I

SUMMARY OF THE INVENTION The present invention is directed to a shadow-mask type color cathode ray tube in which a plurality of electron beams originally aligned in one plane, are deflected horizontally and vertically while being kept aligned in a common plane and are caused to scan an outwardly projecting screen having spherical or cylindrical curvature or the like. The beams pass through a shadow mask to reach thescreen and the transmission factor of the shadow mask is increased to provide for enhanced brightness in the reproduced picture.

Accordingly, one'object of this invention is to provide an improved shadow mask.

Another object of this invention is to provide an improved shadow mask in which a plurality of'apertures are arranged in a particular pattern.

Another object of this invention is to provide a novel color cathode ray tube in which an electron beam exactly impinges on a predetermined color dot.

Another object of this invention is to provide a color cathode ray tube which is bright and free from color misregistration.

Another object of this invention is to provide a color cathode ray tube which employs an in-line gun.

Still another object of this invention is to provide a color cathode ray tube employing an improved shadow mask having a plurality of apertures in a particular pattern and in which color dots on the screen are closely packed in its peripheral portion.

Other objects, features and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings.

7 BRIEF DESCRIPTION OFTHE DRAWINGS FIG. 1 is a perspective view, partlycut away, showing certain geometric relations in a cathode ray tube;

FIG. 2 is a schematic diagram of a shadow mask used in a conventional shadow-mask type color cathode ray tube;

FIGS. 3A and 3B are schematic diagrams showing the relative arrangement of Phosphor dots on the screen perpendicular to the central axis of a cathode ray tube employing the shadow mask depicted in FIG.

. FIG. 4 is a schematic diagramshowing the relative arrangement of the Phosphor dots on a spherical screen of a cathode ray tube using the shadow mask shown in FIG. 2;

FIGS. 5A, 5B and 5C show, onenlarged scale the relative arrangement of the Phosphor dots on a screen in accordance with this invention;

FIG. 6 is a schematic diagram illustrating one example of a shadow-mask for explaining this invention;

FIG. 7 is an enlarged schematic diagram showing the relative arrangement of the Phosphor dots on a spherical screen when using the mask shown in FIG. 6;

FIG. 8 is a schematic diagram illustrating another example of a shadow mask for explaining this invention;

FIG. 9 is a schematic diagram showing the relationship between co-ordinatesand the pitches of aperture alignment lines of the shadow mask for explaining this invention;

FIG. 10 is an enlarged schematic diagram showing the relative arrangement of the Phosphor dots on the screen; I

FIG. 11 shows geometrical relations for explaining the shape of the apertures of the mask of this invention;

and

'FIG. 12 is a schematic diagram, for explaining the orientation of apertures in this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of this invention, a description will be given first of a shadow mask color cathode ray tube, generally indicated by 11 in FIG. 1, which is adapted such that three electron beams 12, 13 and 14 modulated, respectively, with red, green, and blue picture signals are arranged in line in a common horizontal plane 15. The beams are deflected by deflecting means (not shown) horizontally and vertically in a common plane 16 perpendicular to the central axis of the tube and are thereby caused to scan an outwardly curved spherical screen 18 through a shadow mask 17. In this case, the relationship between apertures 19 of the shadow mask 17 and phosphor dots on the screen 18 is of prime importance. This critical relationship will be discussed hereinafter reference to the drawings. 1

The relationship between mask apertures and screen dots will be described first in connection with a conventional type of shadow mask 1 depicted in FIG. 2, in which assumed horizontal and vertical lines X X X1, 0 1 X2, 3- and a Y2, Y1, 0 Y1, Y2, Y are drawn on the shadow mask 1 as viewed from the z-axis direction. The shadow mask 1 is of the type having apertures 2 located at intersections of evennumber horizontal and vertical lines X X X and Y Y Y and at intersections of oddnumber horizontal and vertical lines X X X and Y3, Y1, Y3

Utilizing such a conventional arrangement, the first assumption is that the phosphor screen 3 is a surface perpendicular to the central axis of the tube and that red, green and blue phosphor dots D D and D,, on

oeooa 001 l with the screen 3 are formed by a well-known light or electron beam printing method employing a light or electron beam passing through the horizontal and vertical deflection center of the beam. The phosphor dots D D and D have a diameter and form triplets of picture elements for each aperture 2 of the mask 1. These triplets are sequentially arranged on the horizontal lines. X X X X X X X in the form of horizontal rows as shown in FIGS. 3A and 3B. In view of the requirement for closely packed hexagonal arrays of the phosphor dots D D and D on the phosphor screen 3, the pitch Lx of adjacent vertical columns of apertures of the shadow mask 1 is selected to be V3 times the pitch Ly of adjacent horizontal rows of apertures.

In a shadow mask tube 11 (FIG. 1) having a spherical screen and using an in-line gun, the beam triplets passing through individual apertures 19 are tilted relative to the original alignment of the three beams as shown in FIG. 4. This phenomenon is referred to as the twist of in-line beam triplets. The twist phenomenon is a purely geometrical effect caused by the combination of in-line alignment of three beams and a spherical screen. Considering the coordinate system illustrated in FIG. I, the three beams l2, l3 and 14 passing through the aperture 19 of the shadow mask 17 define the flat plane 16 which is parallel to the x-axis of the tube and which makes an angle of (i /(the angle of vertical deflection) to the 1-2 plane. This flat plane 16 intersects the spherical screen 18 which has the center 0 on the zaxis. The in-line beam triplet 10 thus falls on an intersection line 1, which is an elliptical arc as viewed from the z-axis direction and is expressed as follows.

2 tam 0 y tan a tan0 =y/ R -x R+L Thus, it follows that where 0 is the angle of twist measured from the positive x-axis counterclockwise. The approximate form of the equation (2) is With such an arrangement as has been described above, however, in the case where the diameter of the phosphor dots D D and D on the phosphor screen is selected to be the same as that (1) previously described with respect to FIG. 3, and in view of the requirement for the closely packed hexagonal arrays of the dots, the phosphor dots D D and D corresponding to one of the horizontal rows of apertures 2 overlap those of adjacent horizontal rows of apertures as shown in FIG. 5A because of the fixed relative arrangements of adjacent apertures. To avoid this overlap, the diameter of the apertures of the shadow mask is decreased for increases in the angle 6 and the diameter (1) of the phosphor dots on the screen 3 is selected correspondingly. Thus, in a conventional shadow mask with an in-line gun, the masking tolerance considerably decreases as a consequence of the twist phenomenon of the beam triplets (FIG. 5A).

To avoid this decrease in masking tolerance, the present inventors have previously proposed in the copending United States patent application Ser. No. 877,183, filed Nov. 17, 1969, now abandoned, a shadow mask of the type in which the horizontal alignment lines of the apertures are barrel-shaped; and the vertical alignment lines of the apertures are pincushioned. These horizontal and vertical alignment lines are orthogonal to each other, and the apertures are located at the intersections of the horizontal and vertical alignment lines. The primary object of the prior invention was to compensate the twist phenomenon completely. This object was met by providing an appropriate aperture pattern on the shadow mask. In this prior invention, a horizontal row of the aligned apertures of the spherically-pressed shadow mask and the line passing through the deflection centers of the three electron beams had to be included on a single flat plane. Considering the fact that the radius of the spherically pressed shadow mask is nearly equal to the radius R of the panel inner surface, neglecting the length of the gap between the shadow mask and the panel inner surface as compared with L, the horizontal alignment lines of the apertures were elliptical arcs given by the equation (1), which is the solution of the differential equation of the geometrical twist. A conversion of the integral constant 6 in equation 1 yields to the following expression.

12 (RL) -2(RL) R y where, y 0 for y,,

yo is a parameter which is the intercept of the y-axis by the curve.

The group of arcs of ellipses (Eq. 4) form a barrelshaped group of curves X X X,, X X,, X X as shown in FIG. 6. The vertical alignment lines of the apertures must be made pin-cushioned" so as to be orthogonal to the horizontal alignment lines throughout the shadow mask plane.

The vertical alignment lines can be obtained by solving the following differential equation, which is the inverse and has the opposite sign of the equation of geometrical twist (Eq. 2).

The solution of the equation (5) is obtained as follows.

where x is a parameter which is the intercept of the xaxis by the curve. I Thus, curves obtained from equation (6) are orthogonal to the group of curves obtained from equa-,

This is the pin-cushioned group of circular arcs Y Y Y Y Y,', Y Y .as shown in FIG. 6.

The equations (4), (6and (7) were derived on the basis of a spherically pressed shadow mask. These equations describe the alignment lines of apertures on the spherically pressed shadow mask when viewed from the z-axis direction. However, considering the experimental result showing that when a flat shadow mask is pressed into a nearly spherical plane, the displacement of the aperture position occurs almost only in the zdirection and the displacement in the x-y plane is negligibly small, these equations can be interpreted to mean the alignment lines of apertures of a flat (prepressed) shadow mask.

The foregoing description has also assumed that the phosphor screen 3 is spherical but the same approach can be followed in the case in which the screen is a cylindrical surface extending in a vertical direction. In this case, however, the relationship of the inclination angle of the horizontal row of the triplet of the phosphor dots D D and D for each aperture 2 of the mask 1 to the horizontal line is as follows.

dy E R -a: (Ia-mm which corresponds to equation (2).

Accordingly, in this case the horizontal alignment lines of the apertures are made barrel-shaped; and the vertical alignment lines are made pin-cushioned" so as to be orthogonal to the horizontal alignment lines throughout the shadow mask plane. The apertures are positioned at the intersections of the horizontal and vertical alignment lines, as described above. The curve of the horizontal alignment lines is obtained by solving the differential equation (Eq. 8) to obtain an equation corresponding to equation (4) and by satisfying the resulting equation. The curve of the vertical alignment lines is obtained by solving the following differential equation, which is the inverse, and has the opposite sign, of equation (8):

3:; xy (Eq. 9)

The equation corresponds to equation (6). By solving Although theforegoing discussion has described the shadow mask of the aforementioned copending application in connection with the case where the electron beams respectively corresponding to red, green and blue colors enter the position of the horizontal and vertical deflection means while being aligned in a common horizontal plane, the mask is also applicable to the case where these electron beams enter the position of the deflection means while being aligned in a common vertical plane. In this case it is necessary, of course, to form the apertures at intersections of the horizontal alignment lines made pin-cushioned and the vertical alignment lines made barrel-shaped and to exchange the curves of the horizontal and vertical alignment lines.

However, the pitches of the apertures 2 on the horizontal and vertical alignment lines X and Y on the mask 1 are respectively x and I' (x 3 y peculiar to the xand y-axis. The apertures on each line are arranged at regular intervals and the pitches of the apertures 2 of the vertical alignment lines are gradually increased according to the distance from the center of the mask 1, while the pitches of the apertures 2 of the horizontal alignment lines are gradually decreased according to the distance from the center of the'mask 1. This does not result in the aforementioned relationship that the pitch Lx of adjacent vertical columns of apertures of the mask 1 be VT times the pitch Ly of adjacent horizontal rows of apertures at places remote from the center of the mask 1.

Consequently, the horizontal rows of triplets of phosphor dots D D and D laid down on the screen 3 at places remote from the center of mask 1 are angularly displaced relative to the horizontal lines and do not overlap adjacent dots, as depicted in FIG. 7. The vertical spacings of the phosphor dots are reduced as compared with the vertical spacing at the center of the screen, and the horizontal spacings of the dots are enlarged as compared with the horizontal spacing at the center. However, at locations even further remote from the center, this spacing does not fully satisfy the requirement for closely packed hexagonal arrays of phosphor dots and introduces the possibility of deterioration of color purity resulting from overlapping of the phosphor dots of adjacent horizontal rows of the triplets, as shown in FIG. 5c.

In view of the foregoing, the present invention has as one of its objects the improvement of the shadow mask of the construction depicted in FIG. 6 for use with a shadow mask color cathode ray tube of the type in which the red, green and blue electron beams, aligned in a common horizontal plane, are deflected by deflection means horizontally and vertically while in a common plane and are thereby caused to scan an outwardly curved spherical screen through a shadow mask. The shadow mask of this invention is arranged so that the pitches of the vertical alignment lines of the apertures are enlarged toward both ends of the vertical alignment lines of the apertures, and the pitches of the horizontal alignment lines of the apertures are reduced toward both ends of the horizontal alignment lines so that the this differential equation and by satisfying the resulting pitches of the horizontal and vertical alignment lines of equation, the same results as mentioned previously canbe obtained.

the apertures at the corner region of the mask are substantially equal to those at the center of the mask.

A description will be given of the respective enlargement and reduction of the pitches of the horizontal and vertical alignment lines of the apertures from the center of the mask toward both ends of the horizontal and vertical center alignment lines of the mask. The method for obtaining the varying values of the pitches for such pitch distribution, which has been proposed in the aforementioned United States patent application Ser. No. 877,183, filed Nov. 17, 1969, will also be described below.

ln FIG. 9, horizontal and vertical alignment lines running across the aperture 2 at a desired point P on mask 1, based upon the aforementioned equations (4) and (6), designated by Xn and Ym and theintersecting point of the line Xm with the y-axis (Y is indicated by B(O, y,,,) and the intersecting point of the line Yn with the x-axis is identified by A(x,,, 0).

Assume that the co-ordinate of the point P is x(n, m), y(n, m) Since the point P is the intersecting point of the alignment lines Xm and Yn, the aforementioned equations (4) and (6) are expressed as follows, by substituting y and x,, for y and x 0 in equations (4) and (6) respectively, and by approximately solving simultaneous equations derived therefrom.

The process of solving the simultaneous equations derived from the equations (4) and (6) produces a power series of variables such as x /R y /R xy/R x RL, y /RL, xy/RL RL whose numerators are terms of second order with respect to a length on the shadow mask plane and whose denominators are terms of second order with respect to the length of the radius of curvature R of the spherical screen or the distance from the deflection center of the bean to the center of the screen or both of them. The higher order terms are neglected in the approximation for obtaining the equations l0) and (l l since the aforementioned variables are less than 0.2 in practice.

Accordingly, if the pitches of the vertical and horizontal alignment lines of the apertures in the vicinity of the point P are taken as P (n, m) and P (n, m) respectively, they are given by the follow equations.

(ym )/2RL) (y... ym i) (13) In this case, (x,,-x,, l) is the pitch of the vertical alignment lines on the x-axis (X and may be expressed by P (n, 0), while (y,,,-y,,, 1) is the pitch of the horizontal alignment lines on the y-axis (Y and may be expressed by P (0, m). Consequently, the equations l2) and (13) are respectively given by the following equations l4) and With a line y=yx joining the center of the shadow mask 1 with its peripheral region being expressed in the form of a functional equation, the pitches of the vertical and horizontal alignment lines of the apertures P (n, m) and P (n, m) on the line y=yx, which are obtained by the above equations (14) and (15), are

ymz 1 ym 213 2127. 18

P P 0, 0 PV( 0: m) a: 5127. 2122 19 From the equations (10) and (11) the following relation is obtained:

z mam/(1 Considering y='yx, the equation (20) is expressed as follows:

h. 2 s iiL) 21) While, the relation =yx is given by the following equation:

Accordingly, the following equation is obtained from the equations l6) and l 7):

This equation (23) is expressed approximately as follows:

Further, the equations l8) and 19) are respectively expressed as including y and x,,. However, if equation (22) is substituted into the aforementioned equations (10) and (l l) and an approximation similar to that for obtaining equations (10) and (l l) is used equation (18) can be expressed as including only x,, and equation (19) can be expressed including only ym, In this case P,,(n, 0) and P (O, m) are given by the following The equations (25) and (26), thus obtained, respectively represent the pitches of the vertical and horizontal alignment of the apertures on the xand y-axis when P,,(n, m) and H01, m), at thepoint P on the line y=yx on the mask plane, are equal to P,,,(O, and PM), 0) at the center of the mask.

The equations (25) and (26) are expressed as including 7 used-in the line y=yx. If the vertical and horizontal alignment lines of the apertures at the desired point P on the mask plane, given by the equations (14) and (15), are expanded by substituting equations (25) and (26), the equations (14) and (15) are then expressed by the following equations.

M", m) u( )(l /2 L)) 'Yz nIZRL I 27) v( M (mt D) (ym l 'y 2RL)) (28) Accordingly, if 7 used in the line y=yx is selected to be equal to l, the following relation is obtained from the equations (27) and (28).

The equations (2 and (26) are respectively expressed by the follow equations in the forms of x,, and

By substituting the x and y,, into the aforementioned equations (25) and (26) and by utilizing an approximation similar to that used for obtaining the aforementioned equations and (II), the following equa- Although x and y,, are expressed in the following forms based upon the equations (30) and (31 Substituting substituting n and m for the ks in equations (34) and (35), respectively, and integrating the equations by using the relations of equations (32) and (33), the following equations are obtained.

:c =nP (O, 0 (PW n) (36) ym=mPv(0, (M Q m) (37) Since a= [P (0, 0) /6RL and B [P, (O. 0) /6RL, equations (36) and (37reduce to the follow equations:

ym= v( .0)( +B (39) The foregoing has described a preferred construction of the mask for use with the shadow mask color cathode ray tube of the type in which three electron beams for red, green and blue colors are deflected by a horizontal and vertical deflection device horizontally and vertically while maintaining alignment in a common horizontal plane, and are caused to scan an outwardly curved spherical screen.

With the mask construction disclosed in the aforementioned copending application, deterioration of the color purity can be prevented to an appreciable extent but not completely. The overlapping of the phosphor dots, as shown in FIG. 5C, which results in deterioration of the color purity as previously described, can be avoided by depositing the phosphor dots in elliptic form as depicted in FIG. 10. When making the screen by the usual light or electron beam printing method using the light of an electron beam passing through the electron beam deflection center, the formation of such elliptic phosphor dots can be achieved by making the apertures 2 of the shadow mask 1 in an elliptic configuration.

Accordingly, in the present invention the apertures of the mask described above, are formed elliptic so as to eliminate the possibility of deterioration of the color purity. In this case, the apertureat the center of the mask is circular and the longer and shorter axes of the elliptic apertures at other positions are selected to be in predetermined ratios to avoid the possibility of deterioration of the color purity.

The predetermined ratios of the longer and shorter axes of the elliptic apertures can be obtained by the following method.

If the co-ordinate of any point on the mask 1 is taken as P[x(n, m y(n, m) and the pitches of the horizontal and vertical alignment lines of the apertures near the point of the above co-ordinate are respectively taken as P (n, m) and P (n, m), as previously described in connection with FIG. 5, the pitches are expressed by the aforementioned equations (l4) and (I5).

Assume that the phosphor dots at the central portion of the screen 3 are circles and are closely packed as shown in FIG. 3A. If the pitches of the horizontal and vertical alignment lines are respectively taken as P (0, 0) and P (O, 0), the following equations are obtained.

11 where S is the shortest distance between adjacent apertures at the central portion of the mask. Accordingly,

P,,(O, )/P (0, 0) \/3'' (42) in the case of the shadow mask proposed in the aforementioned co-pending application, the pitches of the apertures on the xand y-axes are substantially constant, so that if these horizontal and vertical pitches are respectively taken as P,,(n, 0) and P (0, m), the following equations are obtained.

H( 0)= (0,0) (43) P (0,m)=P (0,0) 44 Since the pitches of the apertures at any point are given by the equations (14) and (15) as previously mentioned, their ratios are expressed as follows:

1 11, m) w.. Pv( 2RL (45 Accordingly, in the case of the mask disclosed in the aforementioned co-pending application, the following equation can be obtained by substituting the equations (42), (43) and (44) into the equation (45).

Pio'ifmf 2RL A comparison of the equation (46) with (42) shows that according to the equation (46) the ratio of the pitches P,,(n, m) and H01, m), at any point on the mask, is greater than that of the pitches P (0, 0) and P (0, 0) at the central portion of the mask.

Therefore, it will be seen that if the aperture 2 of the mask 1 at any point, namely at the point P, is formed with an elliptic shape as depicted in FIG. 11 and if the ratio of its longer and shorter axes is selected to be (1 (x, y,,, )/2RL) in the equation (46), a closely packed array of phosphor dots is obtained and the phosphor dots do not overlap, as can be seen in FIG. 10.

When the apertures 2 are elliptic, if their longer and shorter diameters are respectively taken as a(n, m) and b(n, m), the resulting ratio is as follows:

If the mask proposed in the aforementioned co-pending application is used, the equation (46) is applied to P (n, m)/P n, m) and the equation (42) is used to obtain the following equation.

a( ,m) z n +ym)/ (48) Accordingly, when the mask proposed in the copending application is used, the ratio of the longer and shorter axes of the ellipse at the center of the mask is 1, i.e. the aperes are circular. The ratio becomes greater as the peripheral portion of the mask is approached. If the distance from the center of the mask to the point P is taken as r(n, m), r(n, m) =x,. +y,,., the same elliptic apertures 2 are formed on a concentric circle about the center of the mask as depicted in FIG. 12.

in the case of the mask in which a pitches of the apertures on the xand y-axes respectively decrease and increase, the equation (45) is applied to P (n, m)/P (n, m) of the equation (47) and, in addition the equation 42) is used, which results in the following equation:

z (1 )I m)z 1/ V3) Mn, v( m) (49) Accordingly, in this case the ratio of the longer and shorter axes of the ellipse at the center of the mask is l but the ratios at other portions are determined by the equation (.49).

Thus, the present invention is characterized by the improvements in shadow masks disclosed in the aforementioned co-pending application.

The foregoing description has been made for a spherical phosphor screen 3, but the same is also true when the screen is a cylindrical surface extending in a vertical direction. In this case, however, the relationship of the inclination angle of the horizontal row of the triplet of the phosphor dots D D and D for each aperture 2 of the mask 1 to the horizontal line is as follows:

Equation (50) corresponds to the equation (2).

. Accordingly, in this case the horizontal alignment lines are made barrel-shaped; and the vertical alignment lines of the apertures are made pin-cushioned" so as to be orthogonal to the horizontal alignment lines throughout the shadow mask plane. Apertures are positioned at the intersections of the horizontal and vertical alignment lines. The curve of the horizontal alignment lines is obtained by solving the differential equation (10) to obtain an equation corresponding to the equation (2) and by satisfying the resulting equation. The curve of the vertical alignment lines is obtained by solving the following differential equation, which is the inverse of the equation l0) and is of the opposite sign:

dyldx= [R -x (RL) VR x ]/xy (5]) to obtain an equation corresponding to the equation (9) and by satisfying the resulting equation. Thus, the same results as mentioned heretofore can be obtained.

Although the present invention has been described in connection with the case where the electron beams respectively corresponding to red, green and blue colors enter the position of the horizontal and vertical deflection means while aligned in a common horizontal plane, the invention is also applicable to the case in which these electron beams enter the position of the deflection means while aligned in a common vertical plane. In this case, however, it is necessary, of course, to use a shadow mask having apertures formed at intersections of the horizontal alignment lines made pincushioned and the vertical alignment lines made barrel-shaped and to exchange the curves of the horizontal and vertical alignment lines.

Further, this invention has been described in connection with embodiments in which the screen 3 is either spherical or cylindrical, but it will be understood that the invention is also applicable in case of any desired outwardly curbed screen.

It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of this invention.

We claim as our invention:

1. A shadow mask for use with cathode ray tubes comprising a metal plate, and a plurality of apertures in the metal plate, in which the apertures are located at the intersecting points of a series of barrel-shaped curved lines and a series of pin-cushioned curved lines which are substantially orthogonal to said barrelshaped curved lines at the intersections with the latter, the apertures are circular at the central portion of the shadow mask and elliptical at other areas thereof, the ratio of the longeraxis to the shorter axis of each of the elliptical apertures is a function of the distance of the aperture from the center of the shadow mask, and each of said elliptical apertures has its said longer axis extending substantially parallel to the respective barrelshaped curved line at the passage of the latter through said aperture.

2. A shadow mask for use with cathode ray tubes comprising a metal plate, and a plurality of apertures in the metal plate, in which the apertures are located at the intersecting points of a series of barrel-shaped horizontal curved lines and a series of pin-cushioned shaped vertical curved lines which are substantially orthogonal to said barrel-shaped curved lines at the intersections with the latter, the pitch of the barrelshaped horizontal curved lines increases and that of the pin-cushioned vertical curved lines decreases as the periphery of the shadow mask is approached, the apertures are circular at the central portion of the shadow mask and elliptical at other areas thereof, the ratio of the longer axis to the shorter axis of each of the elliptical apertures is a function of the distance of the apertu're from the center of the shadow mask, and each of said elliptical apertures has its said longer axis extending substantially parallel to the respective barrelshaped curved line at the passage of the latter through the aperture.

3. A color cathode ray tube comprising: means for generating multiple electron beams in a common plane and converging toward a common point; a fluorescent screen defining a first concave surface facing said beam generating means and having deposited thereon ,a plurality of phosphor dot triplets for emitting light in a plurality of colors when impinged uponby the respective electron beams, each of said triplets having the phosphor dots thereof arrayed generally parallel to said common plane of the beams; and a shadow mask located between said screen and the beam-generating means and comprising a metal plate with a plurality of apertures therein for the passage of said beams and being located at the intersecting points of barrelshaped curved lines extending generally parallel to said plane and pin-cushioned curved lines substantially orthogonal to said barrel-shaped curved lines, and said apertures being substantially circular at said central part of said shadow mask and elliptic at other areas thereof and having a ratio of longer diameter to shorter diameter which is a function of the distance from said central part of said mask, said longer diameter of each of said elliptic apertures being substantially aligned with the one of said barrel-shaped curved lines which passes through the respective one of said apertures,

4. The cathode ray tube of claim 3 in which said first concave surface is spherical.

5. The cathode ray tubeof claim 3 in which said first concave surface is cylindrical. 

1. A shadow mask for use with cathode ray tubes comprising a metal plate, and a plurality of apertures in the metal plate, in which the apertures are located at the intersecting points of a series of barrel-shaped curved lines and a series of pincushioned curved lines which are substantially orthogonal to said barrel-shaped curved lines at the intersections with the latter, the apertures are circular at the central portion of the shadow mask and elliptical at other areas thereof, the ratio of the longer axis to the shorter axis of each of the elliptical apertures is a function of the distance of the aperture from the center of the shadow mask, and each of said elliptical apertures has its said longer axis extending substantially parallel to the respective barrel-shaped curved line at the passage of the latter through said aperture.
 2. A shadow mask for use with cathode ray tubes comprising a metal plate, and a plurality of apertures in the metal plate, in which the apertures are located at the intersecting points of a series of barrel-shaped horizontal curved lines and a series of pin-cushioned shaped verticaL curved lines which are substantially orthogonal to said barrel-shaped curved lines at the intersections with the latter, the pitch of the barrel-shaped horizontal curved lines increases and that of the pin-cushioned vertical curved lines decreases as the periphery of the shadow mask is approached, the apertures are circular at the central portion of the shadow mask and elliptical at other areas thereof, the ratio of the longer axis to the shorter axis of each of the elliptical apertures is a function of the distance of the aperture from the center of the shadow mask, and each of said elliptical apertures has its said longer axis extending substantially parallel to the respective barrel-shaped curved line at the passage of the latter through the aperture.
 3. A color cathode ray tube comprising: means for generating multiple electron beams in a common plane and converging toward a common point; a fluorescent screen defining a first concave surface facing said beam generating means and having deposited thereon a plurality of phosphor dot triplets for emitting light in a plurality of colors when impinged upon by the respective electron beams, each of said triplets having the phosphor dots thereof arrayed generally parallel to said common plane of the beams; and a shadow mask located between said screen and the beam generating means and comprising a metal plate with a plurality of apertures therein for the passage of said beams and being located at the intersecting points of barrel-shaped curved lines extending generally parallel to said plane and pin-cushioned curved lines substantially orthogonal to said barrel-shaped curved lines, and said apertures being substantially circular at said central part of said shadow mask and elliptic at other areas thereof and having a ratio of longer diameter to shorter diameter which is a function of the distance from said central part of said mask, said longer diameter of each of said elliptic apertures being substantially aligned with the one of said barrel-shaped curved lines which passes through the respective one of said apertures.
 4. The cathode ray tube of claim 3 in which said first concave surface is spherical.
 5. The cathode ray tube of claim 3 in which said first concave surface is cylindrical. 